Apparatus and method for diamond production

ABSTRACT

An apparatus for producing diamond in a deposition chamber including a heat-sinking holder for holding a diamond and for making thermal contact with a side surface of the diamond adjacent to an edge of a growth surface of the diamond, a noncontact temperature measurement device positioned to measure temperature of the diamond across the growth surface of the diamond and a main process controller for receiving a temperature measurement from the noncontact temperature measurement device and controlling temperature of the growth surface such that all temperature gradients across the growth surface are less than 20° C. The method for producing diamond includes positioning diamond in a holder such that a thermal contact is made with a side surface of the diamond adjacent to an edge of a growth surface of the diamond, measuring temperature of the growth surface of the diamond to generate temperature measurements, controlling temperature of the growth surface based upon the temperature measurements, and growing single-crystal diamond by microwave plasma chemical vapor deposition on the growth surface, wherein a growth rate of the diamond is greater than 1 micrometer per hour.

The present invention claims the benefit of Provisional Application No.60/331,073 filed on November 7, 2001, which is hereby incorporated byreference in its entirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Grant Nos.EAR-8929239 and DMR-9972750 awarded by the National Science Foundation.The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for producingdiamond, and more particularly, for growing diamond using MicrowavePlasma Chemical Vapor Deposition (MPCVD) within a deposition chamber.

2. Description of Related Art

Large-scale production of synthetic diamond has long been an objectiveof both research and industry. Diamond, in addition to its gemproperties, is the hardest known material, has the highest known thermalconductivity, and is transparent to a wide variety of electromagneticradiation. Therefore, it is valuable because of its wide range ofapplications in a number of industries, in addition to its value as agemstone.

For at least the last twenty years, a process of producing smallquantities of diamond by chemical vapor deposition (CVD) has beenavailable. As reported by B. V. Spitsyn et al. in “Vapor Growth ofDiamond on Diamond and Other Surfaces,” Journal of Crystal Growth, vol52, pp. 219-226, the process involves CVD of diamond on a substrate byusing a combination of methane, or another simple hydrocarbon gas, andhydrogen gas at reduced pressures and temperatures of 800-1200° C. Theinclusion of hydrogen gas prevents the formation of graphite as thediamond nucleates and grows. Growth rates of up to 1 μm/hour have beenreported with this technique.

Subsequent work, for example, that of Kamo et al. as reported in“Diamond Synthesis from Gas Phase in Microwave Plasma,” Journal ofCrystal Growth, vol. 62, pp. 642-644, demonstrated the use of MicrowavePlasma Chemical Vapor Deposition (MPCVD) to produce diamond at pressuresof 1-8 Kpa in temperatures of 800-1000° C. with microwave power of300-700 W at a frequency of 2.45 GHz. A concentration of 1-3% methanegas was used in the process of Kamo et al. Maximum growth rates of 3μm/hour have been reported using this MPCVD process.

In the above-described processes, and in a number of more recentlyreported processes, the growth rates are limited to only a fewmicrometers per hour. Known higher-growth rate processes only produce orgrow polycrystalline forms of diamond. Typically, attempts to producesingle-crystal diamond at grown rates higher than about one micrometerper hour result in heavily twinned single crystal diamonds,polycrystalline diamond, or no diamond at all. Further, known processesfor growing diamond usually require low pressures of less than 100 torr.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a an apparatus and amethod for producing diamond that substantially obviates one or more ofthe problems due to limitations and disadvantages of the related art.

An object of the present invention relates to an apparatus and methodfor producing diamond in a microwave plasma chemical vapor depositionsystem at a high growth rate and at moderate pressures.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, anembodiment of the apparatus for producing diamond in a depositionchamber includes a heat-sinking holder for holding a diamond and formaking thermal contact with a side surface of the diamond adjacent to anedge of a growth surface of the diamond, a noncontact temperaturemeasurement device positioned to measure temperature of the diamondacross the growth surface of the diamond and a main process controllerfor receiving a temperature measurement from the noncontact temperaturemeasurement device and controlling temperature of the growth surfacesuch that all temperature gradients across the growth surface are lessthan 20° C.

In another embodiment, a specimen holder assembly for producing diamondincludes a diamond, a heat-sinking holder making thermal contact with aside surface of the diamond adjacent to an edge of a growth surface ofthe diamond, wherein the diamond is slidably mounted within theheat-sinking holder, a stage for receiving thermal energy from theheat-sinking holder, and a first actuator member that can translatealong an axis substantially perpendicular to the growth surface forrepositioning the diamond within the heat-sinking holder.

In another embodiment, a specimen holder assembly for producing diamondincludes a diamond, a heat-sinking holder making thermal contact with aside surface of the diamond adjacent to an edge of a growth surface ofthe diamond, a thermal mass for receiving thermal energy from theheat-sinking holder, wherein the diamond is retained in the heat-sinkingholder by pressure applied through the thermal mass, and a stage forreceiving thermal energy from the heat-sinking holder via the thermalmass.

In accordance with another embodiment of the present invention, a methodfor producing diamond includes positioning diamond in a holder such thata thermal contact is made with a side surface of the diamond adjacent toan edge of a growth surface of the diamond, measuring temperature of thegrowth surface of the diamond to generate temperature measurements,controlling temperature of the growth surface based upon the temperaturemeasurements, and growing single-crystal diamond by microwave plasmachemical vapor deposition on the growth surface, wherein a growth rateof the diamond is greater than 1 micrometer per hour.

In accordance with another embodiment of the present invention, a methodfor producing diamond includes positioning diamond in a holder,measuring temperature of a growth surface of the diamond to generatetemperature measurements, controlling temperature of the growth surfacewith a main process controller using the temperature measurements suchthat all temperature gradients across the growth surface are less than20° C., growing diamond on the growth surface and repositioning thediamond in the holder.

In accordance with another embodiment of the present invention, a methodfor producing diamond includes controlling temperature of a growthsurface of the diamond such that all temperature gradients across thegrowth surface are less than 20° C. and growing single-crystal diamondby microwave plasma chemical vapor deposition on the growth surface at agrowth temperature in a deposition chamber having an atmosphere with apressure of at least 130 torr.

In accordance with another embodiment of the present invention, a methodfor producing diamond includes controlling temperature of a growthsurface of the diamond such that all temperature gradients across thegrowth surface are less than 20° C.; and growing single-crystal diamondby microwave plasma chemical vapor deposition on the growth surface at atemperature of 900-1400° C.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide Per explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram of a diamond production apparatus according to anembodiment of the present invention in which a cross-section ofdeposition apparatus with a specimen holder assembly for holding thediamond stationary during a diamond growth process is depicted.

FIG. 2 a is a perspective view of the deposition apparatus shown in FIG.1.

FIG. 2 b is a perspective view of the diamond and sheath shown in FIG.1.

FIG. 3 is a diagram of a diamond production apparatus according to anembodiment of the present invention in which a cross-section of adeposition apparatus with a specimen holder assembly for moving thediamond during the diamond growth process is depicted.

FIGS. 4 a-4 c depict cross-sectional views of holders or thermal massesthat can be used in accordance with the present invention.

FIG. 5 is a diagram of a diamond production apparatus according toanother embodiment of the present invention in which a cross-section ofa deposition apparatus with a specimen holder assembly for moving thediamond during the diamond growth process is depicted.

FIG. 6 is a flow diagram illustrating a process 600 in accordance withembodiments of the present invention that can be used with the specimenholder assembly shown in FIG. 1.

FIG. 7 is a flow diagram illustrating a process 700 in accordance withembodiments of the present invention that can be used with the specimenholder assembly shown in FIG. 3 or with the specimen holder assemblyshown in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. FIG. 1 is a diagram of a diamond production system 100,according to an embodiment of the present invention, in which adeposition apparatus 102 is depicted in cross-section. The diamondproduction system 100 includes a Microwave Plasma Chemical VaporDeposition (MPCVD) system 104 that contains a deposition apparatus 102as well as reactant and plasma controls 106. For example, the MPCVDsystem 104 can be a WAVEMAT MPDR 330 313 EHP made by Wavemat, Inc. Sucha MPCVD system is capable of producing a 6-kilowatt power output at afrequency of 2.45 GHz, and has a chamber volume of approximately 5,000cubic centimeters. However, the MPCVD system specifications can varywith the scale of a deposition process in terms of size of thedeposition area and/or rate of deposition.

The MPCVD system 104 includes a chamber within the deposition apparatus102 that is at least in part defined by a bell jar 108, which is used insealing the chamber. Prior to MPCVD operations, the air within thechamber is withdrawn. For example, a first mechanical type of vacuumpump is used to draw down the chamber and then a second high vacuum typeof vacuum pump, such as a turbopump or cryopump, further draws out theair inside the chamber. Plasma is generated within the chamber by a setof plasma electrodes spaced apart within the chamber. Neither the pumpsnor the plasma electrodes are illustrated in FIG. 1.

The deposition apparatus 102 also includes a specimen holder assembly120 installed within the chamber of the MPCVD system 104. Typically, aspecimen holder assembly is positioned in the center of the depositionchamber floor 122 of the deposition apparatus 102, as shown in FIG. 1.The specimen holder assembly 120 shown in FIG. 1 is illustrated incross-section. The specimen holder assembly 120 can include a stage 124installed in the floor of the deposition apparatus 102.

As shown in FIG. 1, the stage 120 can be attached to the depositionchamber floor 122 using bolts 126 a and 126 c. The stage 124 can bemolybdenum or any other type of material having a high thermalconductivity. In addition, the stage 124 can be cooled during theprocess of growing diamond by a coolant passing through a coolant pipe128 within the stage 124. The coolant can be water, a refrigerant orother types of fluid with sufficient heat carrying capacity to cool thestage. Although the coolant pipe is shown as having a U-shaped paththrough the stage 124 in FIG. 1, the coolant pipe 128 can have ahelically shaped path or other types of paths within the stage 124 tomore efficiently cool the stage 124.

Positioned on the stage 124 of the specimen holder assembly 120, asshown in FIG. 1, is a set ring 130 having set screws, such as screws 131a and 131 c, for tightening collets 132 a and 132 b around a sheath 134that holds diamond 136. The sheath 134 is a holder, which makes athermal contact with a side surface of the diamond 136 adjacent to anedge of a top surface of the diamond 136. Because collets 132 a and 132b are tightened onto the sheath 134 by screws 131, the sheath 134 holdsthe diamond 136 in a stationary position and acts as a heat-sink toprevent the formation of twins or polycrystalline diamond along theedges of the growth surface of the diamond 136.

The diamond 136 can include a diamond seed portion 138 and a growndiamond portion 140. The diamond seed portion 138 can be a manufactureddiamond or a natural diamond. As shown in FIG. 1, the top surface orgrowth surface of the diamond 136 is positioned within a region of theplasma 141 having a resonant power at a height H above the depositionchamber floor 122. The resonant power can be the maximum resonant powerwithin the plasma 141 or a degree thereof. The top surface or growthsurface of the diamond 136 is initially the diamond seed portion 138 andis then the grown diamond portion 140 as the diamond grows.

As shown in FIG. 1, the top edge of the sheath 134 is at a distance Djust below the top surface or top edges of the diamond 136. The distanceD should be sufficiently large enough to expose the edges of the growthsurface of the diamond 136 to the plasma 141. However, the distance Dcan not be so large as to prevent the heat-sinking effect of the sheath134 that prevents the formation of twins or polycrystalline diamondalong the edges of the growth surface of the diamond 136. Thus, D shouldbe within a specified distance range, such as 0-1.5 mm. The distance Dand the height H, as shown in FIG. 1, are manually set using the screws131 of the set ring 130 by positioning the diamond 136 in the sheath,positioning the sheath in the collets 132 a and 132 b, and thentightening the screws 131.

FIG. 2 is a perspective view of the deposition apparatus shown inFIG. 1. In the center of the deposition chamber floor 122 of FIG. 2 is acircular stage 124 with a central recess 125. As shown in FIG. 2, thestage 124 is held in position by bolts 126 a-126 d. The stage 124 can beformed of molybdenum or other materials having a high thermalconductivity. A set ring 130 with four screws 131 a-131 b is positionedwithin the recess 125 of the stage 124 along with collets 132 a-132 b.In the alternative, the set ring 130 can be bolted to the stage 124 toincrease thermal conductance between the stage and the set ring.

As shown in FIG. 2 a, a rectangular sheath 134, which can either be ashort length of rectangular tubing or a sheet folded into a rectangle,is positioned in the collets 132 a and 132 b with a diamond 136 therein.The sheath 124 can be molybdenum or any other type of material having ahigh thermal conductivity. The screws 131 a-131 d are tightened on thecollets 132 a-132 b such that the sheath 134 is tightened onto thediamond 136 such that the sheath 134 acts as a heat sink on the fourside surfaces of the diamond 136. As shown in FIG. 1, the sheath 134also makes thermal contact to the stage 124. The collets 132 a-132 bmake thermal contact with the stage 124 and serve as thermal masses fortransferring heat from the sheath 134 into the stage 124. The tighteningof the sheath 134 onto the diamond 136 increases the quality of thethermal contact between the diamond and the sheath. As shown in FIG. 1,the sheath 134 can also make thermal contact to the stage 124. Althougha rectangular shape is shown in FIG. 2 a for both the sheath and thediamond, the sheath and the diamond can have any geometric shape such aselliptical, circular or polygonal. The shape of the sheath or holdershould be substantially the same as the diamond.

In the exemplary embodiment of the invention shown in FIGS. 1 and 2 a,the stage 124 can have a diameter of approximately 10.1 cm. and thesheath 134 can be approximately 2.5 cm wide. Regardless of thedimensions selected for the stage and the sheath 134, the thermal massof the stage 122, molybdenum sheath 124, and collets 132 can be adjustedto provide an optimal heat sink for the diamond 136. Additionally, thepath and extent of the coolant pipes 128 can be modified for greatercooling effect, especially if a particularly large diamond is to beproduced. Further, a refrigerant or other low temperature fluids can beused as a coolant.

Molybdenum is only one potential material used in the stage 124, setring 130, collets 132, sheath 134 and other components. Molybdenum issuitable for these components because it has a high melting point, whichis 2617° C., and a high thermal conductivity. In addition, a largegraphite build-up does not tend to form on molybdenum. Other materials,such as molybdenum-tungsten alloys or engineered ceramics, having highmelting points above the process temperature and a thermal conductivitycomparable to that of molybdenum, can alternatively be used instead ofmolybdenum.

Returning to FIG. 1, another component of the diamond production system100 is an noncontact measurement device, such as an infrared pyrometer142, which is used to monitor the temperature of the diamond seed 138and later the grown diamond 140 during the growth process withoutcontacting the diamond 136. The infrared pyrometer 142 can be, forexample, a MMRON M77/78 two color infrared pyrometer from MikronInstruments, Inc. of Oakland, N.J. The infrared pyrometer 142 is focusedon the diamond seed 138 or later on the grown diamond 140 with a targetarea measure of 2 mm. By using the infrared pyrometer 142, thetemperature of the growth surface of the diamond 136 is measured towithin 1° C.

The diamond production system 100 of FIG. 1 also includes an MPCVDprocess controller 144. The MPCVD process controller 144 is typicallyprovided as a component of the MPCVD system 104. As is well-known in theart, the MPCVD process controller 144 exercises feedback control over anumber of MPCVD parameters, including, but not limited to, the processtemperature, gas mass flow, plasma parameters, and reactant flow ratesby using the reactant and plasma controls 106. The MPCVD processcontroller 144 operates in cooperation with a main process controller146. The main process controller 146 takes input from the MPCVDcontroller 144, the infrared pyrometer 142, and from other measuringdevices of other components in the diamond production system 100 andcarries out executive-level control over the process. For example, themain process controller 146 can measure and control coolant temperaturesand/or flow rates of the coolant in the stage using a coolant controller148.

The main process controller 146 can be a general purpose computer, aspecial purpose computing system, such as an ASIC, or any other knowntype of computing system for controlling MPCVD processes. Depending onthe type of main process controller 146, the MPCVD process controller144 can be integrated into the main process controller so as toconsolidate the functions of the two components. For example, the mainprocess controller 146 can be a general purpose computer equipped withthe LabVIEW programming language from National Instruments, Inc. ofAustin, Tex. and the LabVIEW program such that the general purposecomputer is equipped to control, record, and report all of the processparameters.

The main process controller 146 in FIG. 1 controls the temperatures ofthe growth surface such that all the temperature gradients across thegrowth surface of the diamond are less than or equal to 20° C. Precisecontrol over growth surface temperatures and growth surface temperaturegradients prevents the formation of polycrystalline diamond or twinssuch that a large single crystal diamond can be grown. The ability tocontrol all of the temperature gradients across the growth surface ofthe diamond 136 is influenced by several factors, including the heatsinking capability of the stage 124, the positioning of the top surfaceof the diamond in the plasma 141, the uniformity of the plasma 141 thatthe growth surface of the diamond is subjected to, the quality ofthermal transfer from edges of the diamond via the holder or sheath 134to the stage 124, the controllability of the microwave power, coolantflow rate, coolant temperature, gas flow rates, reactant flow rate andthe detection capabilities of the infrared pyrometer 142. Based upontemperature measurements from the pyrometer 142, the main processcontroller 146 controls the temperature of the growth surface such thatall temperature gradients across the growth surface are less than 20° C.by adjusting at least one of microwave power to the plasma 141, thecoolant flow rate, coolant temperature, gas flow rates and reactant flowrate.

FIG. 2 b is a perspective view of the diamond 136 shown in FIG. 1depicting exemplary points P1, P2, P3 and P4 along the growth surface137 of the diamond 136. FIG. 2 b also depicts the distance D between thegrowth surface 137 or top edges 139 of the diamond 136 and an edge 135of the sheath 134. Typically, large temperature variations, in terms oftemperature differences across the growth surface, occur between theedges and the middle of the growth surface of the diamond. For example,larger temperature gradients occur between the points P1 and P2 thanoccur between the points P1 and P3. In another example, largertemperature gradients occur between the points P4 and P2 than occurbetween the points P4 and P3. Thus, controlling temperature of thegrowth surface of the diamond such that all temperature gradients acrossthe growth surface are less than 20° C. should at least take intoaccount a temperature measurement between the middle and an edge 139 ofthe growth surface 137. For example, the main controller 146 may controlthe temperature of the growth surface such that the temperature gradientbetween points P1 and P2 is less than 20° C.

The spot size of the infrared pyrometer can affect the ability tomonitor temperature gradients across the top surface of the diamond andthus the growth rate of the diamond. For example, if the size of thediamond is large in comparison to the spot size of the infraredpyrometer, the temperature at each of the edges of the growth surface ofthe diamond can be outside of the field of view of the infraredpyrometer. Thus, multiple infrared pyrometers should be used for adiamond with a large growing area. Each of the multiple pyrometersshould be focused on different edges about the surface of the diamondand preferably near the corners, if any. Thus, the main processcontroller 146, as shown in FIG. 1, should be programmed to integrateoverlapping fields of view from the multiple pyrometers to produce acontiguous “map” of the temperatures across the diamond's surface orinterpolate between non-overlapping fields of view to a produce aninterpreted “map” of the temperatures across the diamond's growthsurface. In the alternative, the temperature gradient between a singleedge or corner point with respect to the middle of the growth surfacecan be monitored as indicative of the maximum temperature gradient thatexists across the growth surface of the diamond.

In addition to the infrared pyrometer 142 for temperature control, otherprocess control instrumentation may be included in the diamondproduction system 100. Additional process control instrumentation caninclude equipment for determining the type and quality of the diamond136 while the growth process is underway. Examples of such equipmentinclude visible, infrared, and Raman spectrometers, which are optical innature and can be focused on the same point as the infrared pyrometer142 to obtain data on the structure and quality of the diamond whilegrowth is underway. If additional equipment is provided, it can beconnected to the main process controller 146 such that the main processcontroller 146 controls the instrumentation and presents the results ofthe analytical methods along with other status information. Additionalprocess control instrumentation may be particularly useful inexperimental settings, in “scaling up” a process to produce largerdiamonds, and in quality control efforts for an existing diamondproduction system 100 and corresponding process.

As the diamond 136 grows, both the distance D and the height H increase.As the distance D increases, the heat-sinking capacity of the sheath 134for the top edges 139 of the growth surface of the diamond 136 reduces.In addition, characteristics of the plasma, such as temperature and/orconsistency, change as the growth surface of the diamond 136 extendsinto the plasma 141. In the diamond production system 100, the growthprocess is periodically halted so that the position of the diamond 136can be adjusted downward with respect to the sheath 134 to reduce thedistance D, and both the diamond 136 and the sheath 134 can be adjusteddownward with respect to the deposition chamber floor 122 to reduce theheight H. This repositioning allows the diamond growth of on the growthsurface of the diamond 136 to occur within a desired region of resonantpower within the plasma 141, allows the infrared pyrometer 142 and anyadditional instruments to remain focused on the growth surface of thediamond 136, and has the effect of maintaining an efficient thermalcontact for sinking heat from the edges of the growth surface of thediamond 136. However, repeatedly halting the growth process can beinconvenient for large-scale production, and increases the chance ofintroducing contamination into the process if not carefully performed.

FIG. 3 is a diagram of a diamond production apparatus 300 according toan embodiment of the present invention in which a cross-section ofdeposition apparatus 304 with a specimen holder assembly 320 for movingthe diamond 136 during the diamond growth process is depicted. Some ofthe components of diamond production apparatus 300 are substantially thesame as those of diamond production system 100, and thus, the discussionabove with regard to FIG. 1 will suffice to describe those componentslikewise numbered in FIG. 3. For example, the pyrometer 142, depositionchamber floor 122, coolant pipe 128 and bell jar 108 in FIG. 3 aresubstantially the same as those described in FIG. 1.

As show in FIG. 3, the diamond 136 is mounted on a diamond actuatormember 360 within the sheath 134 of the specimen holder assembly 320.The diamond 136 is slidably mounted within the sheath 134 on a diamondactuator member 360 that translates along an axis substantiallyperpendicular to the growth surface. The diamond actuator member 360protrudes through a stage 324 and is controlled from underneath thestage 324 with a diamond control, which is shown as a part of thecoolant and diamond/holder controls 329 in FIG. 3. The diamond actuatormember 360 is or setting the height H between the growth surface of Mediamond 136 and the deposition chamber floor 122. Although the diamondactuator member 360 in FIG. 3 is shown as a threaded rod, the diamondactuator member can be of any geometric shape that enables positioningof the diamond 136 at height or position above the deposition chamberfloor. Those skilled in the art will realize that components placedwithin the bell jar, such as the diamond actuator member 360, should bevacuum compatible so as to avoid problems in maintaining the desiredatmosphere.

The actuator (not shown) for the diamond actuator member 360 is a motor(not shown). However, the actuator can be any one of a number of knowntypes of actuator, depending on the size of diamond that is to be grown,the growth rate, and the level of movement precision required. Forexample, if the diamond 136 is small in size, a piezoelectric actuatormay be used. If the diamond 136 is relatively large or can be grownrelatively large, a motorized computer-controllable actuator ispreferred. Regardless of the particular actuator employed, the mainprocess controller 346 controls the movement of the diamond actuatormember 360 so that the diamond 136 can be automatically moved downwardas diamond growth progresses.

In addition, a holder actuator member 362 protrudes through the stage324 and is controlled from underneath the stage 324 with holder control,which is shown as a part of the coolant and diamond/holder controls 329in FIG. 3. The holder actuator member 362 translates along an axissubstantially perpendicular to the growth surface and is for maintainingthe distance D between an edge of the growth surface of the diamond 136and a top edge of the holder or sheath 134. A diamond production systemcan have a diamond actuator member, a holder actuator member, or acombination of both.

The holder actuator member 362 in FIG. 3 is threaded into the stage 324and the diamond actuator member 360 is threaded into the holder actuatormember 362. By this arrangement, the diamond and holder controls of thecoolant and diamond/holder controls 329 shown in FIG. 3 can move thediamond 136, the sheath 134, or both the sheath 134 and the diamond 136.Although the holder actuator member 362 in FIG. 3 is shown as a threadedcylinder with threading on the inside for the diamond actuator member360 and threads on the outside for threading into the stage 324, theholder actuator member can be of any geometric shape that enablesmaintaining a specified distance range between an edge of the growthsurface of the diamond 136 and the top edge of the holder or sheath 134.Those skilled in the art will realize that components placed within thebell jar, such as the holder actuator member 362 or a combination ofboth the holder actuator member and the diamond actuator member, shouldbe vacuum compatible so as to avoid problems in maintaining the desiredatmosphere.

As shown in FIG. 3, a thermal mass 364 is positioned within a recess ofthe stage 324. The holder or sheath 134 is slidably positioned withinthermal mass 364 such that thermal energy is transferred from the sheath134 to the stage 324. The top surface of the thermal mass 364 can becontoured such that heat can be transferred from the sheath 134 whileminimizing the electrical effect of the thermal mass 364 on the plasma341. Thermal masses 466 a, 466 b and 466 c in FIGS. 4 a-4 c,respectively, are examples of other contoured thermal masses withdifferent cross-sectional shapes, which in the alternative, can be usedin lieu of the thermal mass 364 shown in FIG. 3. A thermal mass can bemade of molybdenum. Other materials, such as molybdenum-tungsten alloysor engineered ceramics, having high melting points above the processtemperature and a thermal conductivity comparable to that of molybdenumcan be used as a thermal mass for transferring heat from a side of thediamond to a stage.

By minimizing the electrical effect of thermal mass 364 on the plasma341, the region within the plasma 341 in which the diamond is grown willbe more uniform. In addition, higher pressure can be used in growingdiamond, which will increase the growth rate of single-crystal diamond.For example, pressures can vary from 130 to 400 torr and single-crystalgrowth rates can be from 50 to 150 microns per hour. Using a higherpressure, such as 400 torr, is possible because the uniformity, shapeand/or position of the plasma 341 are not as readily affected by thermalmass 364, which is contoured to remove heat from the edges of the growthsurface of the diamond and minimizes the electrical effect of thethermal mass 364 on the plasma 341. In addition, less microwave power,such as 1-2 kW, is needed to maintain the plasma 341. Otherwise, a lowerpressure and/or increased microwave power would have to be used tomaintain the uniformity, shape and/or position of the plasma 341.

As the diamond 136 grows, both the distance D and the height H increase.As the distance D increases, the heat-sinking capacity of the sheath 134for the top edges of the growth surface of the diamond 136 decreases. Inaddition, characteristics of the plasma, such as temperature, change asthe growth surface of the diamond 136 extends into the plasma 341. Inthe diamond production system 300, the growth process is halted when thediamond 136 reaches a predetermined thickness since the distance D andthe height H can be controlled by the main process controller 346, viathe coolant and diamond/holder controls 329, using the holder actuatormember 362 and diamond actuator member 360 during the diamond growingprocess. This repositioning, either manually or automatically undercontrol of the controller 144, allows the diamond growth on the growthsurface of the diamond 136 to occur within a desired region of resonantpower within the plasma 341. Further, repositioning allows the infraredpyrometer 142 and any additional instruments to remain focused on thegrowth surface of the diamond 136, and can maintain an efficient sinkingof heat from the edges of the growth surface of the diamond 136.

FIG. 5 is a diagram of a diamond production apparatus 500 according toan embodiment of the present invention in which a cross-section ofdeposition apparatus 504 with a specimen holder assembly 520 for movingthe diamond 136 during the diamond growth process is depicted. Some ofthe components of diamond production apparatus 500 are substantially thesame as those of diamond production system 100 and 300, and thus, thediscussion above the regard to FIG. 1 and FIG. 3 will suffice todescribe those components likewise numbered in FIG. 5. For example, thepyrometer 142, deposition chamber floor 122, coolant pipe 128 and belljar 108 in FIG. 5 are substantially the same as those described inFIG. 1. In another example, the coolant and diamond/holder controller329 and diamond actuator member 360 in FIG. 5 are substantially the sameas those in FIG. 3.

As shown in FIG. 5, the diamond 136 is mounted on the diamond actuatormember 360 and within a contoured thermal mass 566, which acts as aholder. By placing the diamond 136 directly within the contoured thermalmass 566, thermal efficiencies for heat-sinking the diamond 136 areincreased. However, the plasma 541 may be more easily affected since thewhole contoured thermal mass is moved by the holder actuator 562 in thestage 524 with a diamond holder control, which is shown as a part of thecoolant and diamond/holder controls 329 in FIG. 3. Thus, the mainprocess controller 546 should take into account such a factors forappropriately controlling the plasma and/or other parameters of thegrowth process. In the alternative, the convex thermal mass 364 shown inFIG. 3, the slant-sided thermal mass 466 b in FIG. 4 b, aslant-sided/cylindrical apex thermal mass 466 c in FIG. 4 c or othergeometric configurations can be used m lieu of the concave thermal mass566, in FIG. 5.

FIG. 6 is a flow diagram illustrating a process 600 in accordance withembodiments of the present invention that can be used with specimenholder assembly shown in FIG. 1. The process 600 begins with step S670in which an appropriate seed diamond or a diamond in the process ofbeing grown is positioned in a holder. In the specimen holder assembly120 of FIG. 1 for example, the diamond seed portion 138 is placed in asheath 134 and the screws 131 a-131 d are tightened by an operator.Other mechanisms can be used to maintain both the sheath and diamond inposition, such as spring loaded collets, hydraulics or other mechanismscan be used in exerting a force against the holder or sheath.

As referred to in step S672, the temperature of the growth surface ofthe diamond, either the diamond seed or grown diamond, is measured. Forexample, the pyrometer 142 in FIG. 1 takes a measurement of the growthsurface, which is the top surface of the growing diamond portion 140,and provides the measurement to the main process controller 146. Themeasurement is taken such that a thermal gradient across the growthsurface of the diamond 136 can be determined by the main processcontroller or at least the temperature of an edge of the growth surfaceof the diamond are inputted into the main process controller.

The main process controller, such as main process controller 146 shownin FIG. 1, is used in controlling the temperature of the growth surface,as referred to in S674 in FIG. 6. The main process controller controlsthe temperature by maintaining thermal gradients of less than 20° C.across the growth surface. While controlling the temperature of thegrowth surface, a determination is made to whether the diamond should berepositioned in the holder, as shown in step S675 of FIG. 6. If the maincontroller can not control the temperature of the growth surface of thediamond such that all temperature gradients across the growth surfaceare less than 20° C. by controlling the plasma, gas flows and coolantflows, then the growth process is suspended so that the diamond can berepositioned in the holder, as shown in step S678 of FIG. 6, for betterheat-sinking of the diamond and/or better positioning of the diamondwithin the plasma. If the main controller can maintain all of thethermal gradients across the growth surface of the diamond to be lessthan 20° C., then the growing of the diamond on the growth surfaceoccurs as shown in step S676 of FIG. 6.

Measuring the temperature of a growth surface of the diamond,controlling temperature of the growth surface and growing diamond on thegrowth surface occurs until it is determined that the diamond should berepositioned, as shown in FIG. 6. Although measuring, controlling,growing and the acts of determining are shown and described as steps,they are not necessarily sequential and can be concurrent with oneanother For example, the step of growing diamond on the growth surfacecan occur while measuring the temperature of a growth surface of thediamond and controlling temperature of the growth surface are occurring.

The repositioning of the diamond, as referred to in step S678, can bedone manually or with a robotic mechanism. In addition, a determinationcan be made of whether the diamond has reached a predetermined ordesired thickness, as shown in step S673 of FIG. 6. The determinationcan be based on an actual measurement via mechanical or optical devices.In another example, the determination can be based on the length ofprocessing time in view of known growth rates for the process. If thediamond has reached the predetermined thickness, then the growingprocess is complete, as referred to by step 680 in FIG. 6. If thediamond has not reached the predetermined thickness, then the growthprocess is started again and continues with measuring the temperature ofa growth surface of the diamond, controlling temperature of the growthsurface and growing diamond on the growth surface until it is determinedthat the diamond needs to be repositioned, as shown in FIG. 6.

FIG. 7 is a flow diagram illustrating a process 700 in accordance withembodiments of the present invention that can be used with specimenholder assembly shown in FIG. 3 and FIG. 5. The process 700 begins withstep S770 in which an appropriate seed diamond, which can be a growndiamond, manufactured diamond, natural diamond or combination thereof,is positioned in a holder. In the specimen holder assembly 320 of FIG. 3for example, the diamond seed portion 138 is placed with in sheath 134on the diamond actuator member 360, as shown in FIG. 3. In anotherexample of a specimen holder assembly, the diamond seed portion 138 isplaced within a contoured thermal mass 566 on the diamond actuator 360,as shown in FIG. 5.

As referred to in step S772, the temperature of the growth surface ofthe diamond, either the diamond seed or a newly grown diamond portion onthe diamond seed, is measured For example, the pyrometer 142 in FIG. 3takes a measurement of the growth surface, which is the top surface ofthe growing diamond portion 140, and provides the measurement to themain process controller 346. In another example, the pyrometer 142 inFIG. 5 takes a measurement of the growth surface, which is the topsurface of the seed diamond portion 138, and provides the measurement tothe main process controller 546. The measurement is taken such thatthermal gradient across the growth surface of the diamond can bedetermined by the main process controller or at least the temperaturesof an edge and the middle of the growth surface are inputted into themain process controller.

A main process controller, such as main process controller 346 or 546,is used in controlling the temperature of the growth surface, asreferred to in S774 in FIG. 7. The main process controller controls thetemperature of the growth surface of the diamond such that alltemperature gradients across the growth surface are less than 20° C.while controlling the temperature of the growth surface, a determinationis made to whether the diamond needs to be repositioned in the holder,as shown in step S775 of FIG. 7. If the main controller can not maintainthe temperature of the growth surface of the diamond such that alltemperature gradients across the growth surface are less than 20° C. bycontrolling the plasma, gas flows and coolant flows, then the diamond isrepositioned while the diamond is growing as shown in FIG. 7 with the“YES” path from step S775 to both of steps S776 and S778. Byrepositioning the diamond within the holder, the heat-sinking of theedges of the growth surface is improved. In addition, the growth surfacecan be positioned within an optimal region of the plasma having aconsistency for maintaining all of the thermal gradients across thegrowth surface of the diamond to be less than 20° C. If the maincontroller can maintain all of the thermal gradients across the growthsurface of the diamond to be less than 20° C., then the growing of thediamond on the growth surface occurs without repositioning as shown inthe “NO” path from step S775 to step S776 of FIG. 7.

Measuring the temperature of a growth surface of the diamond,controlling temperature of the growth surface, growing diamond on thegrowth surface and repositioning the diamond in the holder occurs untilit is determined that the diamond has reached a predetermined thickness.As referred to in step S773 of FIG. 7, if a determination is made ofwhether the diamond has reached a predetermined or desired thickness.The determination can be based on an actual measurement via mechanicalor optical devices. For example, a tracking program which records thedepth or the amount in terms of distance that the diamond had to berepositioned during the growth process. In another example, thedetermination can be based on the length of processing time in view ofknown growth rates for the growth process. If the diamond has reachedthe predetermined thickness, then the growing process is complete, asreferred to by step 780 in FIG. 7. If the diamond has not reached thepredetermined thickness, then the growth process continues withmeasuring the temperature of a growth surface of the diamond,controlling temperature of the growth surface, growing diamond on thegrowth surface and repositioning the diamond in the holder until it isdetermined that the diamond needs to be repositioned, as show in the“NO” path from S773 to within S774 of FIG. 7.

When implementing processes 600 and 700, diamond growth is usuallycontinued as long as a “step growth” condition can be maintained. Ingeneral, the “step growth” condition refers to growth in which diamondis grown on the growth surface of the diamond 136 such that the diamond136 is smooth in nature, without isolated “outcroppings” or twins. The“step growth” condition may be verified visually. Alternatively, a lasercould be used to scan the growth surface of the diamond 136. A change inlaser reflectance would indicate the formation of “outcroppings” ortwins. Such a laser reflectance could be programmed into the mainprocess controller as a condition for stopping the growth process. Forexample, in addition to determining if the diamond is a predeterminedthickness, a determination can also be made of whether a laserreflectance is being received.

In general, the methods in accordance with exemplary embodiments of thepresent invention are designed to create large, high-quality diamondswith increased [100] growth rates. The process temperature may beselected from a range of about 900-1400° C.; depending on the particulartype of single-crystal diamond that is desired or if oxygen is used.Polycrystalline diamond may be produced at higher temperatures, anddiamond-like carbon may be produced at lower temperatures. During thegrowth process, a pressure of about 130-400 torr is used, with a methaneconcentration in the range of 6-12% methane. A hydrocarbon concentrationgreater than 15% may cause excessive deposition of graphite inside theMPCVD chamber. A 1-5% N₂/CH₄ added to the reactant mix creates moreavailable growth sites, enhances the growth rate, and promotes {100}face growth. Other aspects of the invention can be understood in greaterdetail from the following examples.

EXAMPLE 1

A diamond growth process was conducted in the above-described MPCVDchamber in FIG. 1. First, a commercial 3.5×3.5×1.6 mm high pressure hightemperature (UPHT) synthetic type Ib diamond seed was positioned in thedeposition chamber. The diamond seed has polished, smooth surfaces thatwere ultrasonically cleaned with acetone. The deposition surface waswithin two degrees of the {100} surface of the diamond seed.

Then, the deposition chamber was evacuated to a base pressure of 10⁻³torr. The infrared pyrometer 142 was focused though a quartz window atan incident angle of 65 degrees on the growth surface of the diamond andhad a minimum 2 mm² diameter spot size. Diamond growth was performed at160 torr pressure using gas concentrations of 3% N₂/CH₄, and 12% CH₄/H₂.The process temperature was 1220° C., and gas flow rates were 500 sccmH₂, 60 sccm CH₄, and 1.8 sccm N₂. Deposition was allowed to continue for12 hours.

The resulting diamond was 4.2×4.2×2.3 mm³ unpolished, and representedabout 0.7 mm of growth on the seed crystal that was grown at a growthrate 5 microns per hour. The growth morphology indicated that the <100>side growth rate was faster than the <111> comer growth rate. The growthparameter, α, was estimated at 2.5-3.0.

The deposited diamond was characterized using x-ray diffraction (XRD),Raman spectroscopy, photoluminescence (PL) spectroscopy and electronparamagnetic resonance (EPR). The X-ray diffraction study of theresulting diamond conformed that it was a single crystal, with a smalldegree of polycrystallinity localized at the top edges of the diamond.Visible/near infrared transmission spectra of the MPCVD grown diamondand seed diamonds confirm that nitrogen is incorporated effectively intothe crystal structure. Raman spectroscopy demonstrates that the top faceof the MPCVD grown diamond has different optical characteristics thanthe seed diamond but has the same internal stress.

A number of MPCVD diamonds were produced according to the guidelines ofExample 1 while varying the described process temperature. Theseexperiments demonstrate the process temperature ranges for producingvarious types of diamond in the growth process according embodiments ofthe present invention. Table 1 sets forth the results of theseadditional experiments.

TABLE 1 Process temperatures for various types of diamond TemperatureRange Type of Diamond Produced <1000° C. Spherical, black diamond-likecarbon (DLC) 1000-1100° C. Smooth dark brown 1100-1200° C. Brown1200-1220° C. Smooth, yellow tint growth 1220-1400° C. Step-flow typewith pyramid like octahedra tinted yellow >1300° C. Twinned orpolycrystalline diamond

EXAMPLE 2

A high-quality, pure CVD single crystal diamond over 0.6 mm in thicknesswas created substantially in accordance with the procedure of Example 1above by adding a small amount (1-3%) of oxygen and lowering the growthtemperature to 900 degrees Celsius. The added oxygen allows a lowergrowth temperature, which removes the nitrogen-related impurities andreduces the silicon and hydrogen impurity levels. The growth rate usingthis process is approximately 10 m/hr, less than that of Example 1 butstill greater than; conventional processes.

The colors of diamond formed by the methods discussed above be changedby annealing. For example, a yellow of brown diamond can be annealedinto a green diamond. Additional information with regard to the diamondproduced in the examples described above is in a paper by the inventorsentitled “Very High Growth Rate Chemical Vapor Deposition ofSingle-Crystal Diamond” Proceedings of the National Academy of theSciences, October 1, 2002, volume 99, no. 20., pages 12523-12525, whichis hereby incorporated by reference in its entirety. Diamond produced bythe above methods and apparatus will be sufficiently large, defect freeand translucent so as to be useful as windows in high power laserapplications or as anvils in high pressure apparatuses.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

1.-64. (canceled)
 65. In a method for diamond production, comprisingcontrolling temperature of a growth surface of the diamond such that alltemperature gradients across the growth surface are less than 20° C.;and growing single-crystal diamond by microwave plasma chemical vapordeposition on the growth surface at a temperature of 900-1400° C. in adeposition chamber having an atmosphere with a pressure of at least 130torr, the modification wherein said atmosphere includes oxygen.
 66. Themethod of claim 1, wherein said atmosphere further includes hydrogen andMethane.
 67. The method of claim 2, wherein said atmosphere furtherincludes nitrogen.
 68. The method of claim 3, wherein said atmosphereincludes 1-5% nitrogen per unit of hydrogen and 6-12% methane per unitof hydrogen.
 69. The method of claim 4, wherein said atmosphere includes1-3% oxygen per unit of hydrogen.